Tool-use induces morphological updating of the body schema

Experimental brain research, 2014

The goal of this study was to elucidate the underlying mechanisms of hand and tool grasping control. We assumed that there is a single principle-governing grasping control irrespective of its effectors and that the degree of prior experience of the effector determines the smoothness of aperture control. Eight participants performed a reach-to-grasp task with four different effectors: index finger and thumb, middle finger and thumb, chopsticks, and a scissor-like tool. Although we employed different effectors with large mechanical variations and different degrees of prior use, maximum grip aperture was scaled as a function of object size and appeared at almost the same timing in all four types of grasping movements. Moreover, reaching time did not substantially differ among grasping conditions. However, plateau duration of the aperture profile differed by effector. Plateau duration was the longest in the unfamiliar scissor-like tool grasping condition. There was no difference between...

Zeitschrift für Psychologie, 2012

This research evaluated how the inertial properties of a tool influence tool-using actions. Grip patterns and movements of 3-, 4-, and 5year-old children and adults were recorded while hammering. Results revealed that both number of pegs driven and movement amplitude increased developmentally and changed as a function of inertial properties of the tool but other aspects of motor control (i.e., period, grip position) did not. This suggests that both children and adults were able to discriminate and modulate only those parameters that had the largest impact on performance (i.e., the delivery of force with the hammer). Even though the ability to adjust tool movements as tool characteristics change is evident during preschool years, the ability to do so did not reach adult levels and appears to continue to develop beyond preschool.

Experimental Brain Research, 1993

This study assessed the reach to grasp movement and its adaptive response to a perturbation of object size. In blocked trials, subjects (n = 12) were instructed to reach 35 cm to grasp and lift a small- (0.7 cm) or large-diameter (8 cm) cylinder. Under an unconstrained condition (condition 1), no instructions as to the type of grasp to adopt were given. Subjects thus naturally used a precision grip (PG) for the small cylinder and whole hand prehension (WHP) for the large cylinder. Under condition 2, subjects were instructed to utilize a PG for grasps of both the large and small cylinders. For condition 3, the instruction was to use WHP irrespective of object size. Kinematic organization was determined with analysis of the recordings of active markers placed on the wrist, thumb, and three fingers. For condition 1 the results showed a temporal arrangement of both components (transport and manipulation) which differed from that of conditions 2 and 3. In perturbed trials, illumination shifted from the small to large cylinder or vice versa. With condition 1, subjects automatically switched from one grasp to another with no or little increase of movement duration. This was generally achieved by an earlier temporal setting of peak wrist deceleration. For conditions 2 and 3, where a change of aperture was required, movement duration was prolonged without adaptation of earlier transport component parameters. It is concluded that the adaptive responses to a change of distal patterning also affect the organization of the proximal component. Assessment of grasps constrained by instructions may lead to interpretations of central control of the reach to grasp movement which differ from those obtained by assessing more natural prehensile patterns.

Experimental Brain Research, 2008

Objects can be grasped in several ways due to their physical properties, the context surrounding the object, and the goal of the grasping agent. The aim of the present study was to investigate whether the prior-to-contact grasping kinematics of the same object vary as a result of diVerent goals of the person grasping it. Subjects were requested to reach toward and grasp a bottle Wlled with water, and then complete one of the following tasks: (1) Grasp it without performing any subsequent action; (2) Lift and throw it; (3) Pour the water into a container; (4) Place it accurately on a target area; (5) Pass it to another person. We measured the angular excursions at both metacarpalphalangeal (mcp) and proximal interphalangeal (pip) joints of all digits, and abduction angles of adjacent digit pairs by means of resistive sensors embedded in a glove. The results showed that the presence and the nature of the task to be performed following grasping aVect the positioning of the Wngers during the reaching phase. We contend that a oneto-one association between a sensory stimulus and a motor response does not capture all the aspects involved in grasping. The theoretical approach within which we frame our discussion considers internal models of anticipatory control which may provide a suitable explanation of our results.

When using a tool, proximal action effects (e.g., the hand movement on a digitizer tablet) and distal action effects (e.g., the cursor movement on a display) often do not correspond to or are even in conflict with each other. In the experiments reported here, we examined the role of proximal and distal action effects in a closed loop task of sensorimotor control. Different gain factors perturbed the relation between hand movements on the digitizer tablet and cursor movements on a display. In the experiments, the covert hand movement was held constant, while the cursor amplitude on the display was shorter, equal, or longer, and vice versa in the other condition. When participants were asked to replicate the hand movement without visual feedback, hand amplitudes varied in accordance with the displayed amplitudes. Adding a second transformation (Experiment 1: 90°-rotation of visual feedback, Experiment 2: 180°-rotation of visual feedback) reduced these aftereffects only when the discrepancy between hand movement and displayed movement was obvious. In conclusion, distal action effects assimilated proximal action effects when the proprioceptive/tactile feedback showed a feature overlap with the visual feedback on the display.

Human dexterity with tools is believed to stem from our ability to incorporate and use tools as parts of our body. However tool incorporation, evident as extensions in our body representation and peri-personal space, has been observed predominantly after extended tool exposures and does not explain our immediate motor behaviours when we change tools. Here we utilize two novel experiments to elucidate the presence of additional immediate tool incorporation effects that determine motor planning with tools. Interestingly, tools were observed to immediately induce a trial-by-trial, tool length dependent shortening of the perceived limb lengths, opposite to observations of elongations after extended tool use. Our results thus exhibit that tools induce a dual effect on our body representation; an immediate shortening that critically affects motor planning with a new tool, and the slow elongation, probably a consequence of skill related changes in sensory-motor mappings with the repeated use of the tool.

Current Biology, 2010

Skillful tool use requires knowledge of the dynamic properties of tools in order to specify the mapping between applied force and tool motion . Importantly, this mapping depends on the orientation of the tool in the hand. Here we investigate the representation of dynamics during skillful manipulation of a tool that can be grasped at different orientations. We ask whether the motor system uses a single general representation of dynamics for all grasp contexts or whether it uses multiple grasp-specific representations. Using a novel robotic interface [4], subjects rotated a virtual tool whose orientation relative to the hand could be varied. Subjects could immediately anticipate the force direction for each orientation of the tool based on its visual geometry, and, with experience, they learned to parameterize the force magnitude. Surprisingly, this parameterization of force magnitude showed limited generalization when the orientation of the tool changed. Had subjects parameterized a single general representation, full generalization would be expected. Thus, our results suggest that object dynamics are captured by multiple representations, each of which encodes the mapping associated with a specific grasp context. We suggest that the concept of grasp-specific representations may provide a unifying framework for interpreting previous results related to dynamics learning.

Zeitschrift für Psychologie/ …, 2012

This research evaluated how the inertial properties of a tool influence tool-using actions. Grip patterns and movements of 3-, 4-, and 5year-old children and adults were recorded while hammering. Results revealed that both number of pegs driven and movement amplitude increased developmentally and changed as a function of inertial properties of the tool but other aspects of motor control (i.e., period, grip position) did not. This suggests that both children and adults were able to discriminate and modulate only those parameters that had the largest impact on performance (i.e., the delivery of force with the hammer). Even though the ability to adjust tool movements as tool characteristics change is evident during preschool years, the ability to do so did not reach adult levels and appears to continue to develop beyond preschool.

New Ideas in Psychology

Modern technologies progressively create workplaces in which the execution of movements and the observation of their consequences are spatially separated. Challenging workplaces in which users act via technical equipment in a distant space include aviation, applied medical engineering and virtual reality. When using a tool, proprioceptive/tactile feedback from the moving hand (proximal action effect) and visual feedback from the moving effect point of the tool, such as the moving cursor on a display (the distal action effect) often do not correspond or are even in conflict. If proximal and distal feedback were equally important for controlling actions with tools, this discrepancy would be a constant source of interference. The human information processing system solves this problem by favoring the intended distal action effects while attenuating or ignoring proximal action effects. The study presents an overview of experiments aiming at the underlying motor and cognitive processes and the limitations of visual predominance in tool actions. The main findings are, that when transformations are in effect the awareness of one’s own actions is quite low. This seems to be advantageous when using tools, as it allows for wide range of flexible sensorimotor adaptations and – may be more important – it evokes the feeling of being in control. Thus, the attenuation of perceiving one’s own proximal action effects is an important precondition for using tools successfully. However, the ability to integrate discordant perception-action feedback has limits, especially, but not only, with complex transformations. When feature overlap between vision and proprioception is low, and when the existence of a transformation is obvious proximal action effects come to the fore and dominate action control in tool actions. In conclusion action–effect control plays an important role in understanding the constraints of the acquisition and application of tool transformations.